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is the 67 bettle the only year that interchanges parts for the 74 thing ie:
tranny, engine., shifter parts

The tranny will interchange with any IRS Beetle or Super Beetle which means 1969-79 non-Mexican variety. The Thing in stock form has different gearing than its Type 1 brethren.

The '74 Thing had a 1600 engine standard. There are lots of Beetle engines that will interchange. In the US, the Beetle had a 1500 engine for 1967 but it will interchange. Things (I believe) had an AH-coded engine but that doesn't matter too much if you are only looking for interchangeability.

Thing seats interchange (without seat track modifications) with a '71 Beetle. There are other years.

The air cooled VW parts that interface with the Thing are contained in a long list of VWs. This interface document is contained on the RoMTOC Thing Data CD Check it out at www.romtoc.com/datacd.html